Activation of smooth muscle cell (SMC) proliferation in response to vascular injury is a widely appreciated vascular problem in clinical medicine, but its basis remains obscure. Our hypothesis is that abnormal posttranslational modification of proteins makes a major contribution to the initiation of activated smooth muscle cellular proliferation associated with vascular neointimal formation following vascular injury. We are particularly interested in the possibility that O-GlcNAcylation of YY1, significantly elevated in the neontimal smooth muscle cells, regulates the YY1-Rb interaction and downstream transcription promoting gene expression that triggers smooth muscle cellular proliferation. We are interested in the possibility that the phosphorylation of Rb at specific amino acids also inhibits the YY1-Rb complexation contributing to the activation of smooth muscle cellular proliferation. The goal of this project is to identify how O-glycosylation of YY1 regulates the YY1-Rb interaction and the transcriptional changes that occur in SMC transition from quiescence to active proliferation. Aim 1: Determine the specific sites of YY1 O-GlcNAcylation in growth arrested and in growth stimulated SMC cultures. The position of O-GlcNAc attachments to YY1 in the fractions will be determined by applying a combination of automated triple quadruple and ion trapping tandem mass spectroscopy. Aim 2: Analysis of YY1 O-GlcNAcylation in response to vascular balloon injury in a rat carotid artery model. The rate and the position of YY1 O-glycosylation 2 days, 4 days, and 8 days after rat balloon injury will be determined. Aim 3: Structure-based site-directed mutagenesis for the identification of the YY1-Rb binding surface and its regulation by Rb phosphorylation. The phosphorylated Ser/Thr residues on pRb that inhibit YY1 binding will be identified. Aim 4: Determine how O-GlcNAcylation influences cellular YY1 functions applying flow cytometry, gene expression regulation, and chromatin immunoprecipitation (ChIP).